Well I got an error when I tried to add a webpart using STSADM, the thing that suprised me that I managed to do it a couple of hours earlier. Only difference was that I was publishing the webpart on a 'updated' virtual server (hostname was changed). Luckily using Google'as my best friend, I found the solution ;)
Amazing how many things can go wrong. As a mental note-to-self: If I ever end up again with weird errors like 'The configuration database could not be updated.' then the problem is likely due to a change in the site configuration: SSL added, domain name change, IP change, etc. To fix: check web parts: C:\Program Files\Common Files\Microsoft Shared\web server extensions\60\BIN>stsadm -o enumwppacks this will show to what sites the web parts are linked to reinstate the site configuration in IIS remove the packs stsadm -o deletewppack -nameThanks Rexy!
make the changes to the site configuration reïnstall the packs Likely theirs an easier fix, but can't be bothered to find out.